Federal authorities were at the apartment of deceased bombing suspect Tamerlan Tsarnaev on Sunday, executing a search warrant, an FBI spokeswoman said.

Amanda Cox said, "There is court-authorized law enforcement activity" at the home in Cambridge, Massachusetts, that Tsarnaev shared with his wife and young daughter.

Workers in white hazmat suits were at the apartment, CNN affiliate WCVB reported.

Cox said the search stopped for the day in the early afternoon. It was not immediately clear whether workers had taken anything from the home.

On Friday, a source briefed on the investigation said investigators found explosives residue in the small apartment.

It has turned up in at least three places, the source said: the kitchen table, the kitchen sink and the bathtub.

Tsarnaev's younger brother, Dzhokhar Tsarnaev, has said they built the bombs there, U.S. law enforcement officials briefed on the progress of the investigation said.

Photos: Suspects tied to Boston bombings 23 photos

Photos: Suspects tied to Boston bombings23 photos

Suspects tied to Boston bombings – Dias Kadyrbayev, left, with Boston Marathon bombing suspect Dzhokhar Tsamaev in a picture taken from the social media site VK.com. Kadyrbayev is expected to plead guilty August 21 to charges in connection with removing a backpack and computer from Tsamaev's dorm room after the April 2013 bombing, according to a defense lawyer.

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Photos: Suspects tied to Boston bombings23 photos

Suspects tied to Boston bombings – Bombing suspect Tamerlan Tsarnaev was killed during the shootout with police in Watertown, Massachusetts, on April 19, 2013. He is pictured here at the 2010 New England Golden Gloves.

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Photos: Suspects tied to Boston bombings23 photos

Suspects tied to Boston bombings – Dzhokhar Tsarnaev was captured in a Boston suburb on April 19, 2013, after a manhunt that shut down the city. In July, he pleaded not guilty to killing four people and wounding more than 200.

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Photos: Suspects tied to Boston bombings23 photos

Suspects tied to Boston bombings – From left, Azamat Tazhayakov and Dias Kadyrbayev went with Boston bombing suspect Dzhokhar Tsarnaev to Times Square in this photo taken from the social media site VK.com. A federal grand jury charged Tazhayakov and Kadyrbayev with obstructing justice and conspiracy to obstruct justice relating to the removal of a backpack from Tsarnaev's dorm room after the bombings. Tazhayakov was convicted of conspiracy and obstruction charges in July 2014. He faces up to 25 years in prison at his sentencing in October. He has filed an appeal.

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Suspects tied to Boston bombings – Robel Phillipos, a U.S. citizen, was also arrested on May 1, 2013. He was charged with lying to federal agents about the bombing, according to court papers.

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Suspects tied to Boston bombings – Phillipos, Tazhayakov and Kadyrbayev are accused of removing items from Tsarnaev's dorm room after the bombings on April 15, 2013. The items they took included a backpack containing fireworks that had been "opened and emptied of powder," according to the affidavit.

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Suspects tied to Boston bombings – The FBI released photos and video on April 18, 2013, of two men identified as Suspect 1 and Suspect 2 in the deadly bombings at the Boston Marathon. They were later identified as Dzhokhar Tsarnaev, 19, and his brother Tamerlan Tsarnaev, 26.

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Suspects tied to Boston bombings – Boston Police released surveillance images of Dzhokhar Tsarnaev at a convenience store on April 19, 2013.

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Suspects tied to Boston bombings – The FBI tweeted this photo on April 19, 2013, and urged Watertown residents to stay indoors as they searched for the second suspect.

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Suspects tied to Boston bombings – The FBI released photos and video on April 18, 2013, of two men it called suspects in the deadly bombings and pleaded for public help in identifying them. The men were photographed walking together near the finish line.

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Suspects tied to Boston bombings – A man identified as Suspect 2 appeared in this photograph by bystander David Green, who took the photo after completing the Boston Marathon. Green submitted the photo to the FBI, he told Piers Morgan in an interview.

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Suspects tied to Boston bombings – The man identified as Suspect 2 appears in a tighter crop of David Green's photo.

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Tsarni said he was the only family member at the funeral home and had not had contact with Katherine Russell, Tamerlan's widow.

The funeral home owner, Peter Stefan, said he still has yet to find a cemetery willing to accept the body for burial.

A day earlier, he had said that if no gravesite is found, he plans to ask the government to find a grave.

Three cemeteries that Stefan contacted said they feared reprisals, but the funeral home owner said you can't pick and choose when it comes to a burial.

"This is what we do in a civilized society, regardless of the circumstances," Stefan said. "As I told some of them, at the immediate moment, you may fear (reprisal), but later on, when things calm down, people are going to resent you because you didn't do it."

Tsarnaev's death certificate has yet to be filed with the Boston city clerk, and there is no burial plot, according to the funeral home.

The city manager of Cambridge said Sunday he would not allow Tsarnaev to be buried in the city if requested by the funeral director or Tsarnaev's family.

"The difficult and stressful efforts of the citizens of the City of Cambridge to return to a peaceful life would be adversely impacted by the turmoil, protests, and widespread media presence at such an interment," City Manager Robert W. Healy said in a statement.

Tsarnaev died April 19 after he and his brother, Dzhokhar Tsarnaev, shot a university police officer to death, carjacked an SUV and hurled bombs at officers pursuing them, according to authorities.

A few days earlier -- April 15 -- he and his younger brother allegedly bombed the Boston Marathon, killing three and wounding more than 260.

CNN obtained a copy of Tamerlan Tsarnaev's death certificate, which lists the cause of death as "gunshot wounds of torso and extremities" and "blunt trauma to head and torso."

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The document notes that Tsarnaev was shot by police and run over and dragged by a car. It lists the manner of death as homicide and notes that he was "DOA," or dead on arrival.

Authorities have said his younger brother may have run him over as they resisted arrest days after the marathon attacks.

Separately, 12 people remained hospitalized with bombing-related injuries on Saturday, according to a count by CNN. None was in serious condition.

Also, the frantic manhunt more than two weeks ago for the surviving bombing suspect drew the attention of gun rights advocates at their convention in Houston.

National Rifle Association Executive Vice President Wayne LaPierre said residents were "imprisoned" in their homes with no means to protect themselves while police searched for the younger Tsarnaev.

"How many Bostonians wished they had a gun two weeks ago?" he asked.

"Boston proves it. When brave law enforcement officers did their job in that city so courageously, good guys with guns stopped terrorists with guns," he said.

'Everyone deserves to be buried'

Tamerlan Tsarnaev's body remained unclaimed until Thursday, when Tsarni, who had previously publicly condemned his alleged attacks, had a funeral parlor pick up the body.

Tsarni had decried the bomb suspects as "losers" after the attacks.

Their parents in Dagestan have said they will not fly his body back to Russia for burial, spokeswoman Heda Saratova said.

WCVB reported that the hearse that picked up Tsarnaev's body ferried it to a funeral home 30 miles from Boston, near the Rhode Island state line.

Residents of North Attleboro, Massachusetts, took to the streets to boo Tsarnaev when they heard about the presence of the corpse in their town, The Sun Chronicle reported.

Others took to social media to vent anger at the funeral home for accepting the body. It was later transported to Stefan's funeral home, Graham Putnam & Mahoney Funeral Parlors in Worcester.

"Everyone deserves to be buried," Stefan said.

The marathon bombings

Authorities say the brothers carried out the Boston Marathon bombings using explosive devices made with pressure cookers.

Dzhokhar Tsarnaev, 19, is being held at a federal Bureau of Prisons medical facility in Devens, Massachusetts, charged with using a weapon of mass destruction, which carries the death penalty.

He is being treated for gunshot wounds to the head, neck, legs and hands that he received in the shootout with police that led to his brother's death.

Other target, possiblecover-up

The marathon was not the original target, the law enforcement officials said. The brothers had set their sights on a suicide attack on the city's massive Independence Day celebration, which draws about 500,000 people and is televised nationally.

But the bombs were ready sooner than anticipated, and a day or two before the Boston Marathon, they changed their plans, the officials said.

They spoke on the condition that their names not be used because they were not authorized to discuss the matter with the media.

One key question involves whether intelligence, law enforcement and homeland security agencies could have done more in their investigation of Tamerlan Tsarnaev in recent years before the attack and whether they shared information effectively enough. An independent government review is under way.

In an interview with Univision published on its website on Saturday, President Barack Obama said that cooperation among agencies can always get better. But he again defended U.S. efforts.

"I think we can continue to improve and refine how we're engaging and countering terrorist activity," Obama said. "I don't think it's fair to say though that law enforcement dropped the ball."

It is very difficult to prevent attacks when dealing with individuals who are self-radicalized and not part of a massive conspiracy or network, he said about the current belief of investigators looking at the origins of the Boston bombing.

Tamerlan's widow; Dzhokhar's friends

Tamerlan Tsarnaev's widow, Russell, has remained largely out of view since her husband's death, staying in her parents' Rhode Island home.

Three of Dzhokhar Tsarnaev's friends have been accused of covering for the bombing suspects.

Azamat Tazhayakov and Dias Kadyrbayev, both from Kazakhstan, were charged Wednesday with conspiring to discard potentially incriminating items from Dzhokhar Tsarnaev's dorm room. Robel Phillipos, a U.S. citizen, was charged with making false statements to investigators.

All three are accused of removing items from Tsarnaev's dorm room after the bombings. According to FBI affidavits released this week, they left with the backpack and Vaseline -- which Tazhayakov believed could be used to make bombs -- and Tsarnaev's laptop.

Investigators found the backpack, fireworks and Vaseline in a landfill last week after a two-day search.

The laptop was turned over by Kadyrbayev on April 19, the same day the FBI raided the apartment he shared with Tazhayakov, Kadyrbayev's attorney Robert Stahl said.

The FBI is examining the laptop, two federal law enforcement officials told CNN.

Authorities have said they believe the Tsarnaev brothers acted alone but are investigating whether they could have learned from or been aided by terror groups, including groups overseas.